Add comprehensive tests for multi-machine support

[GoldenBadger]

Issue by DarraghGriffin
Wednesday Jan 31, 2018 at 17:38 GMT
Originally opened as CPSSD/cerberus#338

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We need tests for multi-machine support that effectively test running a map-reduce across multiple workers. This can likely be accomplished using docker containers on a single machine, however it is necessary to simulate latency when communicating between the workers/master and also when reading the input files.

An initial test can be based on the sprint three demo.